linux-kernel - [PATCH v2 1/3] tty: Add functions for handling flow control chars

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Date:   Fri,  8 Apr 2022 14:39:52 +0300
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     linux-serial@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org,
        Gilles Buloz <gilles.buloz@...tron.com>,
        Johan Hovold <johan@...nel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: [PATCH v2 1/3] tty: Add functions for handling flow control chars

Move receive path flow control character handling to own function
and a helper.

This seems cleanest approach especially once skipping due to lookahead
is added. Its downside is the duplicated START_CHAR and STOP_CHAR
checks.

No functional changes.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
---
 drivers/tty/n_tty.c | 34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index efc72104c840..90b3e06cbeb1 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1220,21 +1220,33 @@ n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
 		process_echoes(tty);
 }
 
+static bool n_tty_is_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
+{
+	return c == START_CHAR(tty) || c == STOP_CHAR(tty);
+}
+
+/* Returns true if c is consumed as flow-control character */
+static bool n_tty_receive_char_flow_ctrl(struct tty_struct *tty, unsigned char c)
+{
+	if (!n_tty_is_char_flow_ctrl(tty, c))
+		return false;
+
+	if (c == START_CHAR(tty)) {
+		start_tty(tty);
+		process_echoes(tty);
+	} else if (c == STOP_CHAR(tty)) {
+		stop_tty(tty);
+	}
+
+	return true;
+}
+
 static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
 {
 	struct n_tty_data *ldata = tty->disc_data;
 
-	if (I_IXON(tty)) {
-		if (c == START_CHAR(tty)) {
-			start_tty(tty);
-			process_echoes(tty);
-			return;
-		}
-		if (c == STOP_CHAR(tty)) {
-			stop_tty(tty);
-			return;
-		}
-	}
+	if (I_IXON(tty) && n_tty_receive_char_flow_ctrl(tty, c))
+		return;
 
 	if (L_ISIG(tty)) {
 		if (c == INTR_CHAR(tty)) {
-- 
2.30.2